This invention relates to rolling bearings, and more particularly to rolling bearings long in rolling fatigue life which are effectively used, for instance, in the transmissions or engines of automobiles, agricultural machines, constructing machines or iron and steel machines.
The inner race, outer race and rolling elements of a rolling bearing are made of various alloy steels such as for instance high carbon chromium bearing steel SUJ2. The recent tendency of rolling bearings is to increase loads applied thereto, and to miniaturize them, and accordingly to increase surface pressures given to them. On the other hand, as rotary members are increased in the speed or machines are enclosed in housings, the rolling bearings used in them are increased in operating temperature, and lubricating oil films are not sufficiently formed in the rolling bearings. That is, rolling bearings must operate in severe operating environments.
In the case of rolling bearings used for instance with the transmissions of a variety of machines, they are used with lubricant contaminated by foreign matters such as metal chips, shavings, burrs and/or powder. Those foreign matters in the lubricant damage the inner race, outer races and rolling elements, thus greatly shorten the rolling fatigue life.
In order to solve the above-described problem, the present Applicant has proposed a rolling bearing in which at least one of the inner race, outer race, and rolling elements is made of an alloy steel which contains: at least two selected from the group consisting of 0.2 to 1.7 wt % of Mn, 0.2 to 1.2 wt % of Si, 0.2 to 1.7 wt % of Cr, 0.1 to 0.3 wt % of Mo, and 0.1 to 1.0 wt % of Ni; 0.4 to 0.7 wt % of C; and the remaining wt % of Fe, and is carbo-nitrided so that the sum of the amount of carburizing and the amount of nitriding of the surface portion thereof is 0.35 to 0.6 wt %, and that the sum of the amount of solid-solution carbon and the amount of solid-solution nitrogen of the surface portion thereof is 0.75 to 1.1 wt %, and the hardness of the core portion thereof is H.sub.R C 57 to 64, and the difference in hardness between the surface portion and the core portion is within .+-.H.sub.R C 5 (cf. Japanese Patent Application (OPI) No. 303222/1988 (the term "OPI" as used herein means an "unexamined application").
The rolling bearing thus proposed still has room for improvement in the lengthening of its rolling fatigue life when it is used with a lubricant contaminated by foreign matters. In forming the rolling bearing, its wear resistance or seizure resistance is not particularly taken into account.